Younger Sister Who Crossed the Line

Min-ah lives with her older brother, Woo-jin. She’s obsessed with Woo-jin to the point of obsession and jealous of her new step-sister, Na-jung. Min-ah’s behavior stresses Na-jung, escalating into a marital spat. Ultimately, Na-jung explodes and tells Woo-jin they should break up, and Woo-jin confesses that Na-jung isn’t actually his biological sister.